Pressure gauges and other instruments utilizing a Bourdon tube enjoy very extensive commercial and industrial use and are consequently regarded as high production items. Because of such wide use, they are supplied by a plurality of manufacturers and sold in very price conscious competition. Each manufacturer instinctively strives to reduce product costs by improvements, however marginal, which reduce labor and/or materials that can contribute to cost savings in the end product.
Commonly affording pressure sensitivity in the pressure gauge is the Bourdon tube being a tube of a pressure tight construction having a free end displaceably movable in a well known and predictable manner in response to pressure changes supplied at its inlet. To translate tube movement into values of pressure, a pointer opposite a calibrated dial plate is displaceably driven by the free end of the tube, usually through an amplification device.
Typically, Bourdon tubes of the prior art are formed by shaping stainless or process tubing as a unitary structure comprised of an arcuate displacement portion communicating at one end with a relatively non-displacement portion and terminating at its free end in what is regarded as the displacement tip. The arcuate extent of such displacement portions is characteristically on the order of about 230 degrees to 270 degrees.
While such Bourdon tubes of the prior art have provided reliable and satisfactory performance over the years, it has been realized that the quantity of metal consumed in the manufacture of such tubes for any given operating range can be excessive in that the displacement portions have greater arcuate extent than required to meet performance requirements. Obviously, the use of excess material constitutes waste which in turn translates into added and unnecessary expense for the manufacturer. This problem is further compounded when severe service conditions are encountered requiring the use of more exotic and more costly materials in the manufacture of such tubes. Despite recognition of the foregoing, a ready solution to the problem has not heretofore been known.